The present application relates to an optical interferometer, and in particular to a multi-cavity etalon interferometer useful as a low dispersion optical interleaver filter.
Optical interleavers are becoming a popular tool in dense wavelength division multiplexed (DWDM) communications networks as an interface between components designed for signals with a first wavelength channel spacing and components designed for signals with a second wavelength channel spacing. In the past 200 GHz channel spacing was the norm, but as the demand for increased bandwidth grew, 100 GHz channel spacing became the standard. In the next generation of communications networks 50 GHz channels spacing and even 25 GHz channel spacing will become common place. However, conventional de-multiplexing filters, e.g. dichroic filters, do not have the capability to separate channels that are so closely spaced. Accordingly, optical interleavers are used to separate the closely spaced channels into two sets of channels, which are twice as far apart. This process can continue until the channels are far enough apart for conventional multiplexing to be effective.
Interleavers can take several forms, including Birefringent Crystal Interleavers, Integrated Lattice Filter Interleavers, and Michelson Gires-Tournois (MGT) Interleavers. The present invention relates to Michelson Gires-Tournois Interleavers, such as those disclosed in U.S. Pat. No. 6,169,626 issued Jan. 2, 2001 in the name of Jye-Hong Chen et al, and U.S. Pat. No. 6,252,716 issued Jun. 26, 2001 in the name of Reza Paiam. Both of these references disclose the use of an interferometer, including a beamsplitter and two Gires-Tournois (GT) resonators, for interleaving/de-interleaving optical wavelength channels. Polarization-based versions of the MGT Interleavers are disclosed in U.S. Pat. No. 6,130,971 issued Oct. 10, 2000; U.S. Pat. Nos. 6,169,604 and 6,169,828 issued Jan. 2, 2001; and U.S. Pat. No. 6,215,926 issued Apr. 10, 2001 all in the name Simon Cao. The polarization-based interferometers typically include a polarization beam splitter (PBS) and two GT resonators each with a birefringent waveplate therein. GT etalons with a birefringent waveplate are referred to as BGTs. Single BGT versions of the invention are possible, since orthogonally polarized components of a single beam will effectively xe2x80x9cseexe2x80x9d different resonators, if an appropriate waveplate is provided in the resonator cavity. However, polarization diversity front ends are required in the single BGT versions.
The aforementioned conventional MGT Interleavers provide acceptable chromatic dispersion at 100 GHz; however, unacceptable chromatic dispersion is created at the 50 and 25 GHz level.
An object of the present invention is to overcome the shortcomings of the prior art by providing an optical interferometer for use as an interleaver, which displays relatively low dispersion.
Accordingly, the present invention relates to an interferometer comprising:
a first port for launching a first input optical signal;
a beam splitter for dividing the first input optical signal into first and second sub-beams, and for directing the first and second sub-beams along first and second optical paths, respectively;
a first multi-cavity resonator in the first optical path for re-directing the first sub-beam to interfere with the second sub-beam, the first multi-cavity resonator including a first resonant cavity providing a first dispersion profile to the first sub-beam, and a second resonant cavity for modifying the first dispersion profile resulting in a second dispersion profile for the first sub-beam;
a second multi-cavity resonator in the second optical path for re-directing the second sub-beam to interfere with the first sub-beam forming first and second output beams, the second multi-cavity resonator including a third resonant cavity providing a third dispersion profile to the second sub-beam, and a fourth resonant cavity for modifying the third dispersion profile resulting in a fourth dispersion profile for the second sub-beam, wherein dispersion from the first multi-cavity resonator compensates for dispersion in the second multi-cavity resonator providing less overall dispersion to the first and second output beams;
a second port for outputting the first output signal; and
a third port for outputting the second output signal.
Another aspect of the present invention relates to an interferometer comprising:
a first port for launching a first input optical signal;
first phase-biasing means for introducing an initial phase difference between first and second orthogonally polarized components of the first input optical signal;
a multi-cavity resonator comprising first and second resonant cavities, each of the first and second resonant cavities including second phase biasing means for providing an additional phase difference between the first and second components of the input optical signal, whereby, when the first and second components are recombined, first and second output beams are formed; wherein the first resonant cavity provides first and second dispersion profiles to the first and second components, respectively, and the second resonant cavity modifies the first and second dispersion profiles resulting in third and fourth dispersion profiles, respectively, whereby the dispersion from the first component compensates for the dispersion from the second component, and the first and second output signals have less overall dispersion;
a second port for outputting the first output signal; and
a third port for outputting the second output signal.